The ever-increasing consumption of fossil fuels and their unfavorable burning products, CO2, are leading the society into serious energy shortage and environmental issues. Alternative energy technologies with low CO2 emission are urgently desired to meet the demands. Solid oxide co-electrolysis cell offers a potential way to convert surplus renewable electricity into easily transportable chemical energy by splitting H2O and CO2 into syngas (a mixture of CO and H2), which can be used as feedstock through the subsequent well-established Fischer-Tropsch (F-T) process to produce liquid synthetic fuel.
However, there are still many challenges before it becomes practically feasible. Solid oxide co-electrolysis cell is in principle a concentration cell, which performs according to the gas conditions in both electrode sides. For the current solid oxide co-electrolysis cell system, the cathode is typically composed of Ni-based material, which is easily oxidized losing its electrical and catalytic properties. Thus, some reduced gases such H2 and/o CO are required to feed together with the co-electrolysis reactant CO2 and H2O to maintain the reducing atmosphere in the cathode. Meanwhile, the anode is often directly exposed to air, and the oxygen gas produced during the co-electrolysis is normally emitted as an exhaust or collected as it forms. It is a huge waste or at least not effectively utilized, deserving to generate more commercial values. To make things worse, the current operating conditions for solid oxide co-electrolysis cells can cause an extremely large difference of the oxygen pressure between two electrodes. The oxygen pressure gradient results in a high open circuit voltage up to 1.0 V at 800° C. according to the Nernst equation. It is known, however, that a voltage higher than the open circuit voltage (“OCV” or “VOC”) is required to generate the co-electrolysis. So the current solid oxide co-electrolysis cell has a very low electrolysis efficiency since most of the electricity is consumed to overcome the initial energy barrier resulted from the oxygen pressure gradient not for producing the real electrolysis.